Triangular backup cushion seat



FIG. 1 is a back elevational view;

FIG. 2 is a front elevational view;

FIG. 3 is a top plan view;

FIG. 4 is a bottom plan view;

FIG. 5 is a side elevational view, the other side being a mirror image;

FIG. 6 is a perspective view of a triangular backup cushion seat, showing my new design; and,

FIG. 7 is a perspective view of a triangular backup cushion seat, without the cover for convenience of illustration. 

The ornamental design for a triangular backup cushion seat, as shown and described. 